Scars

Acts 28
³ But when Paul had gathered a bundle of sticks and laid them on the fire, a viper came out because of the heat and fastened itself on his hand. ⁴ When the natives saw the creature hanging from his hand, they began saying to one another, “Undoubtedly this man is a murderer, and though he has been saved from the sea, justice has not allowed him to live.” ⁵ However he shook the creature off into the fire and suffered no harm. ⁶ But they were expecting that he was about to swell up or suddenly fall down dead. But after they had waited a long time and had seen nothing unusual happen to him, they changed their minds and began to say that he was a god.

This is one of my favorite stories.  Paul had been through some hairy situations.  Beaten, imprisoned, hated by his own people, harassed at every turn, shipwrecked, and snake bitten (I hate snakes and would have screamed like a girl and hoped that nobody wrote about it), Paul had scars.  Through all the trials, God never let him down. 
The things we go through leave their mark on us.  Sometimes those marks open doors of opportunity to share the good news of what God is doing. You can try to hide them, which usually doesn't work for long, or you can use them as an opportunity to share how God has been faithful.